1. Field of the Invention
The present invention relates to a Group III nitride compound semiconductor device. The present invention is particularly useful for a Group III nitride compound semiconductor device functioning as a light-emitting device such as a light-emitting diode (LED), a laser diode (LD), or the like. Incidentally, the Group III nitride compound semiconductor device is represented by the general formula AlxGayIn1xe2x88x92xxe2x88x92yN (0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6x+yxe2x89xa61), which includes binary compounds such as AlN, GaN and InN; ternary compounds such as AlxGa1xe2x88x92xN, AlxIn1xe2x88x92xN and GaxIn1xe2x88x92xN (each 0 less than x less than 1); and quarternary compounds such as AlxGayIn1xe2x88x92xxe2x88x92yN (0 less than x less than 1, 0 less than y less than 1, 0 less than x+y less than 1) In this specification, the concept xe2x80x9cGroup III nitride compound semiconductorxe2x80x9d includes a Group III nitride compound semiconductor doped with impurities to form a p-type or an n-type as the conduction type if there is no notice.
The present application is based on Japanese Patent Application No. Hei. 11-353139, which is incorporated herein by reference.
2. Description of the Related Art
The Group III nitride compound semiconductor is a direct transition type semiconductor exhibiting an emission spectrum in a wide range of from ultraviolet to red. The Group III nitride compound semiconductor is applied to a light-emitting device such as a light-emitting diode (LED), a laser diode (LD), or the like. Generally, sapphire is used as a substrate for the Group III nitride compound semiconductor. The Group III nitride compound semiconductor is formed on the substrate. In this case, a so-called clad layer is provided so that electrons from a negative electrode and holes from a positive electrode make pairs in a light-emitting layer. In the Group III nitride compound semiconductor light-emitting device, AlxGa1xe2x88x92xN (0 less than x less than 1) containing aluminum (Al) is generally used as the clad layer.
FIG. 3 shows a structure of a light-emitting diode (LED) 900 as an example of the background-art Group III nitride compound semiconductor light-emitting device. The light-emitting diode (LED) 900 has a sapphire substrate 901, and an AlN buffer layer 902 formed on the sapphire substrate 901.
An n-type layer 903 of GaN doped with silicon (Si), an n-type clad layer 904 of AlxGa1xe2x88x92xN doped with silicon (Si), and an active layer 905 of a multiple quantum well structure (MQW) made of an alternate lamination of well layers of GayIn1xe2x88x92yN and barrier layers of GaN are formed successively on the buffer layer 902. A p-type clad layer 906 of AlxGa1xe2x88x92xN doped with magnesium (Mg) and a p-type contact layer 907 of GaN doped with magnesium (Mg) are further formed on the active layer 905. An electrode 908A is formed on the p-type contact layer 907. On the other hand, an electrode 908B is formed on the n-type layer 903.
In the above background art, however, then-type and p-type clad layers of AlxGa1xe2x88x92xN (0 less than x less than 1) are apt to crack because the n-type and p-type clad layers are so thick as to be high in elastic constant. Hence, there is a problem that device characteristic runs short.
An object of the present invention is to provide a Group III nitride compound semiconductor device and a Group III nitride compound semiconductor light-emitting device in which the elastic constant of thick layers of AlxGa1xe2x88x92xN (0 less than x less than 1) is reduced so that lowering of device function is avoided.
In order to achieve the above object, according to an aspect of the present invention, there is provided a Group III nitride compound semiconductor device comprising at least three layers of AlxGa1xe2x88x92xN (0 less than x less than 1), and at least three layers of GayIn1xe2x88x92yN (0 less than y less than 1), wherein the AlxGa1xe2x88x92xN layers and the GayIn1xe2x88x92yN layers are laminated alternately.
According to another aspect of the present invention, in the above group III nitride compound semiconductor device, each of the layers of GayIn1xe2x88x92yN (0 less than y less than 1) has a thickness in a range of from 15 nm to 30 nm, inclusively.
According to a further aspect of the present invention, in the above group III nitride compound semiconductor device, the above group III nitride compound semiconductor device is made to be a light-emitting device.
In the Group III nitride compound semiconductor device, a layer requiring a wide band gap demands AlxGa1xe2x88x92xN (0 less than x less than 1). Therefore, when the layer is formed as a multilayer structure of AlxGa1xe2x88x92xN (0 less than x less than 1) and GayIn1xe2x88x92yN (0 less than y less than 1), the layer can be provided as a layer having a wide band gap of AlxGa1xe2x88x92xN (0 less than x less than 1) and having a small elastic constant as a whole. Hence, cracking caused by the temperature change, or the like, at the time of production and use can be suppressed. This effect is particularly remarkable in a layer of AlxGa1xe2x88x92xN (0 less than x less than 1) containing a large amount of Alx. When a plurality of AlxGa1xe2x88x92xN (0 less than x less than 1) layers are formed, total characteristic design of the Group III nitride compound semiconductor device, especially design of the light-emitting layer (composition of AlxGayIn1xe2x88x92xxe2x88x92yN) can be performed more flexibly.
When the thickness of a layer of GayIn1xe2x88x92yN (0 less than y less than 1) is selected to be in a range of from 15 nm to 30 nm inclusively, cracking can be suppressed approximately perfectly while the function of the layer requiring a wide band gap can be kept high. Incidentally, if the thickness is smaller than 15 nm, the effect of reducing the elastic constant of the laminate of layers of AlxGa1xe2x88x92xN (0 less than x less than 1) and layers of GayIn1xe2x88x92yN (0 less than y less than 1) is insufficient. If the thickness is larger than 30 nm, the function of the layer requiring a wide band gap is lowered. The aforementioned device is useful as a light-emitting device such as a laser diode, a light-emitting device, or the like.